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Thread: My Drew Daniel's inspired DIY project.

  1. #31
    Senior Member Rudy Kleimann's Avatar
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    Check yourself, Baron

    Something is wrong with your math here. No other reason than that. Not to worry too much, though, unless your net volume plus damping yields an effective volume that is way off the mark. A little off here and there isn't going to matter much, if at all. Cabinet size is often adjusted from the theoretical to the practical for aesthetic or other reasons, namely size or fit in a particular installation. Your ears will tell you... they are your best test instrument , and the receiver of good vibrations that make the musical experience... never lose sight of this fact while busying yourself with the math and science of it all .

    As Zilch pointed out, actual testing of the finished system is the only way to see what you really, really ended up with. This includes the ear test

    A couple of points:

    Insulation, particularly fiberglass, adds virtual volume by converting the energy in the air from adiabatic (constant heat) to isothermal (constant temperature) which brings about a reduction in the speed of sound. loosely filling a box with insulation can easily increase the effective volume 20%; theoretically it can increase it by 40%. If you were shooting for 5CF, but your tests indicate 7.5CF, something is wrong here, either your physical dimensions are innacurate, or your test method to determine box tuning frequency is wrong. Insulation improves damping, which controls ringing and overshoot when the driver is fed a transient signal. R-11 is fine; I wouldn't use any less than this on the cabinet walls. This should add about 10% virtual volume, or as Drew has commented in the JBL enclosure guide, should about amount to about the same volume displaced by driver(s), bracing, and ports. A little thicker should add all that much more.

    The same size port in a larger box will yield a lower tuned frequency. As Zilch pointed out, the design programs will get you close -if your physical dimensions and volume calculations are accurate. Always start long on the port as long as it is not too close to any obstruction i.e. a cabinet wall or bracing, and cut it to length to hit the actual tuned frequency desired. If your box volume is too big (or you think it is), fill the void with bricks, sandbags, or other solid, inert, incompressible material and give it a listen.

    How exactly are you determining the tuned frequency of your box? You should be able to get close by feeding the woofer a sine wave at 100-200 watts, carefully observing cone movement as you sweep down through the frequencies below 60 Hz. At the box tuned frequency, port output is at maximum (as felt by your hand) while at the same time, the cone movement is at its' minimum (practically stops moving). The accurate method involves an oscilloscope and a resistor (PM me if you have a 'scope and want the setup instructions).
    As you go below the tuned frequency, the cabinet ceases to load the woofer, and cone movement increases rapidly as you continue sweeping down. At this point, STOP! If you continue sweeping down, woofer excursion increases to the point where the voice coil can crash into the rear plate of the magnet and damage the coil. It can also be hard on the spider, surround, or even the cone itself. I've seen cones curl back near the suspension from over-excursion and even develop a circular fatigue line in the paper cone near the dust cap. This quickly leads to driver failure from severe over powering or driving below the ported box frequency. Just because the coil can handle the power doesn't mean you can't break the speaker...

  2. #32
    Senior Member Rudy Kleimann's Avatar
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    Different sized ports???

    Quote Originally Posted by spkrman57
    And also, you can adjust one of the ports by itself and tune it that way instead of messing with all 3 ports.

    Ron
    I don't know about that... I'd plug a port, but I wouldn't have different length ports... seems wrong to me.

  3. #33
    Senior Member Baron030's Avatar
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    Thanks Zilch and Rudy for all of your help.

    Your responses made me really question my test results. So, it forced me to go back to “The Book”. “The Book” in this case is “Testing Loudspeakers” by Joseph D’Appolito.

    The excel chart that I included in my last post was created using a voltage divider technique described in Joseph’s book. For test equipment, I used a freeware computer program called SigJenny and an inexpensive digital multimeter. I have tested accuracy of the SigJenny program, using oscilloscope and I have found it to be very accurate. So, I know that the SigJenny program is not at fault here. Since, I don’t have my computer hooked up to my stereo. I used the SigJenny program to create my own DIY Port Testing CD with each track spaced just 1 hertz apart.

    Getting back to my excel chart, all of the data contained in it is fairly accurate. But, I have completely misunderstood it meaning. After taking some additional impedance measurements, this time with the ports closed, I have now gathered all of the information necessary to properly calculate the enclosure tuning. The missing bit of information is the closed-box resonant frequency of my enclosures, which just happens to be 48 Hertz.

    Fb = box tuning frequency
    Fc = the closed-box resonant frequency
    Fh = the frequency of the higher-frequency impedance peak
    Fl = the frequency of the lower-frequency impedance peak
    Fm = the frequency of the minimum impedance between the two peaks

    Fb = square root of ( (Fh x Fh) + (Fl x Fl) – (Fc x Fc) )
    So, plugging in the data values for my left enclosure into the formula above, the box tuning works out to be:
    38.74 Hz = square root of ((58 x 58) + (21 x 21) – (48 x 48))
    And for the right enclosure tuning works out to be:
    37.23 Hz = square root of ((57 x 57) + (21 x 21) – (48 x 48))

    These numbers come in fairly close to BB6P predicted values for an enclosure with a “heavy” amount of fill. Since, my project has a dog box, there is larger amount of surface area relative to its volume, which may explain why my project comes in with a heavier amount of fill in it.

    Normally, the Fm value is very close to the Fb value. But, in my project, the Fm value appears to be much lower than the Fb value. And that is where I got really confused.

    Over this last week end, I did try to observe at what frequency the cone movement was at its minimum. But, with separate test tones for each frequency, I found this test method next to impossible to judge accurately. So, I think I will stick with the voltage divider method for now.
    Thanks again Zilch and Rudy, you both deserve a cold frosty one.
    Baron030

  4. #34
    RIP 2011 Zilch's Avatar
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    Heh. You are "Golden" on tuning, then....

  5. #35
    Senior Member JBLROCKS's Avatar
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    WOW


    FANTASTIC JOB!!!

  6. #36
    Senior Member UreiCollector's Avatar
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    Amazing cabinet work

    I'm very impressed! These must sound incredible!!
    Frederick "The Urei Collector"

  7. #37
    Senior Member spkrman57's Avatar
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    Final port tuning info????

    I'm curious what the final result on the port length ended up at.

    Ron
    JBL Pro for home use!

  8. #38
    Senior Member Baron030's Avatar
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    Hi Ron

    I have gotten side tracked with the holidays and other projects for a long time now. So, I haven't gotten around to gluing the tubing in place and calling this project done yet. Currently, I got the ports trimmed down to 7.5" long. And my last tests showed that the tuning is still a little below 40 Hz. But, at this point, I realize that I am so very close to hitting the bull's eye that I am not sure if I want to trim the ports any shorter or not.
    Maybe, with some better test equipment, I could be convinced that another ½" may have to come off. But, I am not sure that it would make any real difference in the sound.

    The 2226s now have a great punchy sound and I don't feel the least bit bass deprived, yet.

    Baron030

  9. #39
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    Hello Baron,

    Well done nice workmanship on your enclosures- I love the compression driver support and detailed routing on the front panel and matching routed grill. Make me want to get into a DIY project.
    Best
    Joe Alesi
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

  10. #40
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    Quote Originally Posted by Baron030 View Post
    So, the really big question is this. What to about this virtual volume issue?
    That's why we prototype...

    At least you've experienced first hand why I've harped on proper enclosure tuning, virtual volume and enclosure losses countless times to nothing more than blank stares in return.

    Nice project!
    Quote Originally Posted by Baron030 View Post
    Your responses made me really question my test results. So, it forced me to go back to “The Book”. “The Book” in this case is “Testing Loudspeakers” by Joseph D’Appolito.

    These numbers come in fairly close to BB6P predicted values for an enclosure with a “heavy” amount of fill. Since, my project has a dog box, there is larger amount of surface area relative to its volume, which may explain why my project comes in with a heavier amount of fill in it.
    Good book to have in the personal library.

    BB6P does a nice job.
    Quote Originally Posted by Baron030 View Post
    Currently, I got the ports trimmed down to 7.5" long. And my last tests showed that the tuning is still a little below 40 Hz. But, at this point, I realize that I am so very close to hitting the bull's eye that I am not sure if I want to trim the ports any shorter or not.
    Maybe, with some better test equipment, I could be convinced that another ½" may have to come off. But, I am not sure that it would make any real difference in the sound.

    The 2226s now have a great punchy sound and I don't feel the least bit bass deprived, yet.

  11. #41
    Junior Member Dualbios's Avatar
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    Love this project really is helping me strive to get mine done

  12. #42
    Senior Member Baron030's Avatar
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    Hi Dualbios

    Other then enjoying this system, I have not done much more to enhance the system. In a way, I would not recommend the 2012H driver for your project. This driver has a rising response which does require some additional equalization. It has a strong peak at about 1,000 Hz, which requires a fairly high Q series tank circuit to bring under control. So, it’s not liked a lot around here.

    Also, the 2380a/2446h combination will require a little high frequency shelving boost in the 3,500 to 8KHz range to get a flat response out to the 8Khz crossover point for the 2405 UHF driver. Here is a link to one of my early attempts at a 2012H EQ network, see response number 6: http://www.audioheritage.org/vbullet...read.php?15658

    I know I should post some updates on the EQ networks for this project. So, I will work on that soon. Oh, and for the record I did take red pill and bought “Cliowin 7 Lite”. So, with Clio, I can see just "how deep the rabbit hole goes." I know I am being little silly...

    Baron030

  13. #43
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    Consider scrapping the venting on the mid. You can start by just stuffing the vents, before trying to optimize the sub-enclosure. I'm assuming the tuning is below the XO, and is there for power handling, but really doesn't need it for any reasonable use.

    Any crossover details you can provide?

  14. #44
    Senior Member 1audiohack's Avatar
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    I like 2012's and 2020's but I have never tried to tame them passively. 2123's are a snap though its true.

    About that rabbit hole thing, there is no end, it is infinitely deep, how far you go in is up to you. For some of us it's an obsession, I know I can't stop thinking about it, no matter what I'm doing, audio stuff is running in the background in my mind.

    Cough up that red pill if you can!
    If we knew what the hell we were doing, we wouldn't call it research would we.

  15. #45
    Senior Member Wardsweb's Avatar
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    Very nice indeed. A lot of work but something to be very proud of. Now just enjoy the fruits of your labor.

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